The effect of Zn2+ ion in promoting inhibitive property of phenolphthalein

The inhibition efficiency of phenolphthalein in controlling corrosion of carbon steel immersed in well water has been evaluatedby mass loss method both in absence and presence of zinc ion. A synergistic effect exists between phenolphthalein (PN)and Zn2+. The inhibition efficiency (IE) of the PN – Zn2+ system decreases with increase in immersion period. Addition ofN-Cetyl-N, N, N-Trimethylammlonium bromide (CTAB) sodium dodecyl sulphate (SDS), sodium sulphite (Na2SO3) doesnot change the excellent inhibition efficiency of the PN-Zn2+ system. Polarization study suggests that the Pn-Zn2+ systemfunctions as a mixed inhibitor system. AC impedance spectra reveal the presence of a protective film on the metal surface.FTIR spectra indicate that the protective film consists of Fe2+-PN complex and Zn(OH)2.